Steven T. Manson

Relative intensities in photoelectron spectroscopy of atoms and molecules

The relative intensities of photoelectron lines is discussed. The relationship of observed intensities to angle of observation is considered as are the errors introduced by ignoring the fact that different lines may have different angular distributions. Tables of theoretical results for the angular distribution asymmetry parameter, β, are presented for incident Al Kα, Mg Kα, and Zr Mζ radiation for all atomic ground state subshells of non-zero angular momentum. The application of these results to molecules is discussed.

X-ray emission rates in the hartree-slater approximation

X-ray emission rates for the filling of inner-shell vacancies have been calculated for all elements from Z=6 to Z=100 with nonrelativistic Hartree-Slater wavefunctions. Results are presented for all shells, K, L, … Q, for electric dipole transition only.

Quantum defect values for positive atomic ions

Abstract The asymptotic quantum defects, at the ionization limit, of s, p, d, and f atomic orbitals have been calculated in the Hartree-Slater approximation for all ionization stages of all ions with atomic number Z ⩽ 50.

Atomic Photoelectron Spectroscopy, Part I

Publisher Summary This chapter explains the theoretical photoionization process and experimental techniques involved in the atomic photoelectron spectroscopy. Recently, photoionization was investigated experimentally almost entirely via photoabsorption measurements, but in the last 15 years direct observations of the ejected photoelectrons (photoelectron spectroscopy) have been made in ever-increasing numbers. The angular distribution of the photoelectrons can also be measured using photoelectron spectroscopy. The intensity of a photoelectron line is proportional to the photoionization cross section of that energy. The simplicity of wave functions consisting of single slater determinants—that is, antisymmetric products of one-electron functions can be maintained while still treating exchange correctly. Recent conference proceedings have also contained a wealth of information on the experimental methods of photoelectron spectroscopy. The proceedings of the International Conference on Electron Spectroscopy held in 1971 and the one held in 1974 contain many papers on all the phases of the experimental situation, particularly on photoelectron analysis and detection.

A unique situation for an endohedral metallofullerene

This letter demonstrates for the first time that an endohedral environment, such as the bucky-ball C60, can produce a significant redistribution of oscillator strengths in endohedrally trapped atoms, making the dominant transitions no longer superior but inferior, and also making electron correlations in such atoms act in an opposite way to free atoms. This is exemplified by calculations of the oscillator strengths and photoionization cross sections of the Ca atom trapped inside C60. Also, while photoionization cross sections can undergo dramatic changes on confinement, the photoelectron angular asymmetry parameter n can, in contrast to natural expectation, remain largely unchanged. The random-phase approximation with exchange was employed. We believe these are the first calculations of electron correlations for confined atomic species.

Differential Cross Sections for Ionization of Methane, Ammonia, and Water Vapor by High Velocity Ions,

Cross sections, differential in the energy of secondary electrons, for ionization of methane, ammonia, and water vapor by high energy protons are presented. The results are based on a model that uses photoabsorption and ion impact ionization data to evaluate the coefficients in Bethe’s asymptotic cross section for inelastic scattering of high velocity ions. Model cross sections are compared with previously published data and new data on ionization of methane and water vapor by 3.0 and 4.2 MeV protons. The simple, analytic model should be very useful in transport calculations where differential ionization cross sections over a broad range of primary and secondary energies are needed.

Beyond the dipole approximation: angular-distribution effects in valence photoemission

Angular distributions of valence photoelectrons showing effects due to higher-multipole photon interactions have been measured for the first time. Neon 2s and 2p photoemission exhibits effects beyond the dipole approximation throughout the 250 - 1200 eV photon-energy range studied. The results suggest that any photoemission experiment, on any sample, can be affected at relatively low photon energies, pointing to a general need for caution in interpreting angle-resolved-photoemission measurements.

Satellite lines in photoelectron spectra

Abstract A general theoretical framework is presented for treating satellite line intensities in photoelectron spectra. It is shown that aside from multiplet structure characteristic of open shell systems, satellite lines involve a breakdown of the one-electron or single particle approximation. For any choice of independent electron basis states, this breakdown can be in the form of initial state configuration interaction, final ionic state configuration interaction, or interchannel coupling (configuration interaction) among the various possible photoionization channels (ion plus photoelectron system). This last effect has not been discussed in connection with photoelectron spectroscopy but its consequences can be extremely important.

Photoionization of C60: a model study

Time-dependent density functional theory is used to calculate the total and subshell photoionization cross sections of C60. The core of 60 C4+ ions is smeared into a classical jellium shell before treating the correlated motion of the 240 valence electrons quantum mechanically. The calculation reveals two collective plasmon resonances in the total cross section in agreement with the experiment. It is found that a phase-coherent superposition of amplitudes leading to enhancements in the ionization from various C60 subshells in two distinct energy regions essentially builds the plasmons. While the result shows good qualitative agreement with the experiments, the limitation of the model to describe the data in quantitative detail is discussed.

Atomic Photoelectron Spectroscopy. II

Publisher Summary This chapter provides a comprehensive overview of the atomic photoelectron spectroscopy. It deals primarily with the theory of photoionization, and photoelectron angular distributions and calculations at various levels of approximation. The focus is on the physical implications of each approximation to allow an approximate prior assessment of how well a given calculation would do in a particular situation. An attempt is made to show the variety of phenomena uncovered, their physical explanation, and the predictive powers of the theory by comparison with experiment. From an experimental point of view, making measurements on gaseous atoms or molecules is quite similar and many more measurements of molecules than atoms have been made, since there are so many more gaseous molecules. The chapter concludes with a brief discussion of some very successful recent calculations of molecular photoionization cross sections and angular distributions.